Precisely manufactured machines are available to perform various tooling or manufacturing operations on a workpiece and/or to perform various measurements relative to the workpiece. The machine often will include several members that move relative to the workpiece during the performance of the specified task. At least portions of the machine will be spaced some measurable distance from the workpiece. The machine then may include one or more members that will selectively move into closer proximity to the workpiece or that will move along the workpiece.
Machines that fit the above described general characteristics may be operative to drill, thread, ream, cut or weld a workpiece. Other machines that fit the above described general characteristics are measurement instruments that move relative to the surface of a workpiece to make and record certain measurements that define particular attributes of the workpiece.
As an illustrative example, precise measurement instruments are used in the manufacture of automobiles. More particularly, an early phase in the design of a new automobile model is to produce a full size model of the vehicle. The model will then be analyzed for various aesthetic and engineering characteristics. At some point during this analytical procedure, the precise geometric shape of the model will be recorded to facilitate certain analytical tests, to carry out certain design revisions and to enable various forms to be constructed for use in manufacturing the actual vehicles. One apparatus that is employed to make and record these geometric measurements includes a measuring instrument that moves along one or more rails relative to the model. The measurement instrument includes a probe that follows the contour of the model as the instrument moves along the rail. Movements of the probe are sensed, digitized and stored for subsequent reproduction. After the instrument has completed one longitudinal pass along its rail, the relative height of the instrument may be adjusted a selected amount to enable a second pass relative to the model. This process is continued until the geometric coordinates have been measured for the entire surface of the model.
The above described machining and measuring equipment can be manufactured to achieve extreme precision. However, the actual precision and performance of the machine often depends upon various external factors. For example, the building in which the machine is employed may develop certain sags and shifts that will cause the machine support and the workpiece to move relative to their initial intended positions. In other situations, temperature variations can cause various shifts in the positions of machine or workpiece members relative to one another. In still other situations, gravitational effects on an extended support or arm may cause geometric variations. Another common source of geometric errors results from the inevitable but unintended contact with various machine parts. Such contact can cause a very minor movement in one part of a machine that will be geometrically significant at a location on the machine spaced therefrom.
There are six types of geometric errors that may occur in any of the above described systems. More particularly, the system may exhibit pitch, roll or yaw errors, which define angular variations relative to the three orthogonal axes (X, Y and Z). The machine may also exhibit certain vertical, horizontal or longitudinal displacement errors.
Most of the above described geometric errors can be compensated for if the errors are known. However, the machines themselves generally are unable to identify and measure their own internal geometric errors or errors resulting from shifts in their supporting surfaces. Furthermore, mechanical measurements are imprecise and time consuming.
Laser alignment systems have been developed to facilitate the precise alignment of members relative to one another. These systems generally include a laser source and a target sensitive to the laser source. The target typically is operative to identify the precise point at which it is impinged upon by the laser. The target and/or the laser may also be in communication with a controller which reports and/or records sensed information and which may enable alignment corrections. Examples of alignment systems are shown in: U.S. Pat. Nos. 3,902,810; 4,045,129; 4,297,031; 4,382,680 and 4,566,202, all of which issued to Martin R. Hamar, the applicant herein. The disclosures of the prior patents are incorporated herein by reference. Also of relevance is applicant's copending application Ser. No. 636,835 filed Aug. 1, 1984, the disclosure of which is incorporated herein by reference. Although all of the above described laser alignment devices and systems are extremely effective, none of the systems are capable of effectively assessing all or most of the six possible geometric errors described above.
Accordingly, it is an object of the subject invention to provide an apparatus for accurately measuring geometric errors.
It is another object of the subject invention to provide an apparatus for simultaneously measuring a plurality of different types of geometric errors.
It is an additional object of the subject invention to provide an apparatus that can be readily incorporated into a machine to continuously measure a plurality of possible geometric errors.
Another object of the subject invention is to provide a laser system for assessing a plurality of geometric errors in a machine tool or coordinate measureing machine.